Rituale romanum is latin for “Roman Ritual”. It is a book containing the set of rites and rituals within the Roman Catholic Church which may be led by Catholic priests. First and foremost amongst these is the “liturgy” ie the ritual when mass is held, but there are details of how to hold other events also, such as blessings, baptisms, marriages etc.
It is important to note that in the early days of the Christian church the situation was rather undefined. The birth of the Catholic church was not a sudden event that happened with Christ or during his lifetime (or just after with the resurrection). The “Bible” (or rather the New Testament of the Bible) as compendium of Christ’s life and events was assembled long after Christ was alive, nor is there much evidence that the four gospels were actually hand written and assembled by the apostles themselves, but rather they are a collection of the apostle’s teachings as written by people who had known them or been in their circle. It is rather like asking ourselves whether the Odyssey and Iliad were actually written by Homer or whether they are in fact a written version of a collection of oral tradition….
We can therefore easily see that the writing and assembly of texts such as the Rituale Romanum occurred over time, in much the same way that the rituals held within it were developed over time.